This invention relates to a sound-absorbing material and a cable reel including the same, and more particularly it relates to a sound-absorbing material preferably adapted to be used in a cable reel which is mounted on a steering device for an automotive vehicle and electrically interconnects a stationary member assembly and a movable member assembly through a flat cable.
In an automotive vehicle equipped with an air bag, a cable reel is provided in a steering wheel in order to supply electrical power to an air bag system. For convenience of explanation, such a cable reel will be described below by referring to the drawings. FIGS. 6A to 6C show an example of a conventional cable reel. FIG. 6A is a schematic longitudinal sectional view of a conventional cable reel. FIG. 6B is a perspective view of a conventional sound-absorbing material. FIG. 6C is a fragmentary cross sectional view of the sound-absorbing material shown in FIG. 6B.
As shown in FIG. 6A, the conventional cable reel includes a movable member assembly 10 which rotates together with a steering wheel, and a stationary member assembly 11 which is secured to a stationary shaft on a body frame. The movable and stationary member assemblies 10 and 11 define an annular cable containing chamber 12 which accommodates a flat cable 15 in a coiled manner. Opposite ends of the flat cable 15 in the coiled manner are connected to lead wires which are led out from the movable and stationary member assemblies 10 and 11, respectively, to be connected to an external connector or electrical wires. In such a cable reel, the flat cable 15 is wound in the cable containing chamber 12 when the steering wheel is turned in either a clockwise or counter clockwise direction while the flat cable 15 is unwound in the chamber 12 when the steering wheel is turned in the other direction, so that a device (air bag) on the steering wheel is electrically connected to a power source on the body frame.
However, the cable reel involves a problem in that an unpleasant sliding noise is generated when the lateral opposite edges of the flat cable 15 slide on upper and lower bearing surfaces of the cable containing chamber 12 upon winding and unwinding of the flat cable 15 in the chamber 12. The flat cable 15 vibrates in an axial direction (from an upper to lower direction or from a lower to upper direction) of the steering wheel during idling or driving of the automotive vehicle, thereby giving rise to an unpleasant vibration noise due to collision between the bearing surfaces of the chamber 12 and the lateral opposite edges of the flat cable 15.
Japanese Utility Model Publication No. HEI 6-36040 (1994) discloses a cable reel in which a highly lubricative sheet such as a polytetrafluoroethylene (PTFE) resin or the like is adhered to at least one of bearing surfaces of a cable containing chamber in order to attenuate sliding noise. Also, Japanese Patent Public disclosure No. HEI 8-104471 (1996) discloses a cable reel in which a sound-absorbing material made of a resilient material such as a rubber or the like or a sound-absorbing material with the polytetrafluoroethylene (PTFE) resin is attached to bearing surfaces of stationary and movable member assemblies by means of clamps provided on the surfaces.
A polytetrafluoroethylene resin sheet is adhered by way of PET (polyethylene terephthalate) to a surface of a rubber sheet since the former lacks adhesion to the latter.
Although the polytetrafluoroethylene resin sheet disclosed in Japanese Utility Model Publication No. HEI 6-36040 (1994) can attenuate the sliding noise due to its high lubrication, it cannot reduce noise which is caused by collision of the flat cable with the bearing surfaces of the cable reel due to axial vibrations of the cable in a coiled state. In particular, such an unpleasant collision noise is likely to be accentuated when an engine is idling. On the other hand, the resilient sheet disclosed in Japanese Patent Public Disclosure No. HEI 8-104471 (1996) only slightly attenuates sliding noise, since the lubrication between the flat cable and the resilient sheet is poor, although the sheet can reduce collision or vibration noise.
In a sound-absorbing material 50 shown in FIG. 6C, a rubber sheet 50a having a polytetrafluoroethylene (PTFE) resin sheet 50c provided thereon can attenuate and absorb sliding noise and vibration noise by means of a highly lubricative resin and rubber sheet.
As shown in FIG. 6B, however, a rubber sheet 50a, a polyethylene terephthalate (PET) film 50b and a polytetrafluoroethylene (PTFE) resin sheet 50c must be punched out into an annular shape adapted to be used, since the bearing surfaces of the cable containing chamber 12 is in an annular form. Consequently, this involves much loss of material. In particular, a total cost of the cable reel becomes high since the PTFE resin sheet is expensive.
In addition, the above sound-absorbing material involves a high cost due to an increase in working steps, since the PET film 50b is adhered to the rubber sheet 50a through an adhesive and then the PTFE resin sheet 50c is attached to the PET film 50b by way of an adhesive.
Moreover, the above sound-absorbing material gives rise to a problem in that it reduces a sound-absorbing effect since the hard PET film 50b is interposed between the rubber sheet 50a having a sound-absorbing function and the PTFE resin sheet 50c having a lubricative function. It is difficult to produce the PTFE resin sheet 50c having a low-thickness since it is produced by means of skiving. Consequently, the sheet 50c on the market is usually more than 20 .mu.m. Such a thick PTFE resin sheet 50c in addition to the hard PET film 50b will lower the sound-absorbing function.